The Memory Span Procedure
In a typical test of memory span, a list of random numbers or letters is read out loud or presented on a computer screen at the rate of one per second. The test begins with two to three numbers, increasing until the person commits errors. Recognizable patterns (for example 2, 4, 6, 8) should be avoided. At the end of a sequence, the person being tested is asked to recall the items in order. The average digit span for normal adults without error is seven plus or minus two. However, memory span can be expanded dramatically - in one case to 80 digits - by learning a sophisticated system of recoding rules by which substrings of 5 to 10 digits are translated into one new chunk.
In a backward digit span task, the procedure is largely the same, except that subjects being tested are asked to recall the digits in backward order (e.g., if presented with the following string of numbers "1 5 9 2 3," the subject would be asked to recall the digits in reverse order; in the case, the correct response would be "3 2 9 5 1").
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